In semiconductor chip manufacturing processes, multiple dies (also known as die units) are fabricated on a single wafer. These dies are later separated and packaged into individual chips. The yield of chips from each wafer is not 100% because of defects during the manufacturing process. The number of good die obtained from a wafer determines the yield. Die units are typically transferred from one facility to another, or lot to lot, for various manufacturing and quality control operations.
In order to keep track of the dies, each die unit on a wafer is assigned a unique identifier (Die ID), and each wafer is assigned to a grouping of wafers such as a lot. Wafers in a lot are sometimes tracked as Materials of the lot. Lot and Material objects in the Manufacturing Execution System (MES) are a representation of the physical items in the factory. The die IDs can be of any format and one convention is to use the coordinate position of the dies on the wafer as an identifier (or part of a die's identifier) where the die IDs can (but do not necessarily) contain information regarding the lot that the IDs are in. Any additional information corresponding to the dies are assigned into Additional Strings, which together with the combined Die IDs constitute the die information of the Lot or other Material. For example, users may want to add information such as product, grade, etc. to each die in the lot. Such information can be carried in the Additional strings. When the corresponding elements of the Die ID are matched with the Additional String, the information of the individual die, i.e. its ID and, say, its product can be obtained.
When there is a transfer of at least some of the die units from one lot to another, the corresponding die information along with its wafer and lot information needs to be passed to the new lot. This die information is useful in tracing, at the die unit level, an individual die's history in terms of operation undergone, carrier used for its transportation, the lot it belonged to at various times, and other historical information.
In a conventional assembly operation, die units may be drawn for processing from, for example, a first wafer within a first lot. Alternatively, die units can be drawn from multiple locations. Co-mingling good dies from various locations of a single wafer, from several wafers, and from several wafer lots is what typically occurs during the assembly operation. Unfortunately, whenever die units among multiple wafers and multiple lots are co-mingled, traceability as to a particular die unit is lost. If a die later proves unreliable in the field, it would be beneficial from the viewpoint of the manufacturer to identify the source of the die unit. It would also be desirable to determine how and when the die unit was manufactured. Such indicia could aid the manufacturer in improving the manufacturing process not only after the die units are shipped, but also possibly during tests of the die units before shipment.
Conventional techniques used to trace die units are primarily limited to manipulating die IDs when die units are transferred from one lot to another. Due to the large amount of information often involved and the complexity of this task, this manipulation can be a slow and burdensome process. It would thus be desirous to avoid the cumbersome process of adjusting the die IDs of both the transferred die units in the receiving object, and adjusting the die IDs of the die units remaining in the source object. Accordingly, the present invention is directed to these, as well as other important ends.